Scale reading apparatus for rotatable mirror devices



Dec. 22, 1942. G. HANS'EN 2,305,715

SCALE READING APPARATUS FOR ROTATABLE MIRROR DEVICES Filed Sept. 5, 1939main: \uui imw- J I v V/ in vemor:

S PATENT OFFICE UNITED STATE SCALE READINGAPP ARATUS FOR ROTAT- ABLEltflBROR DEVICES Gerhard Hansen, Jena, Germany: vested in the AlienProperty Custodian Application September 5, 1939, Serial No. 293,462

In Germany September 12, 1938 2 Claims. (01. sa -24) The data obtainedin measuring technics are indicated in most cases by a galvanometer, thedeflections of which are a measure for the magnitudes in question. Theinstrument of this kind which is oldest and most widely used inscientific v to follow a luminous index on a long scale, the observersattention having to be directed permanently to one and the same place inthe instrument.

4. The distance the reading-off device is not to be considerably greaterthan the other dimensions of the instrument.

According to the present invention, the aboveapart of the galvanometerand one instrument. In this instrument a convergent optical system andthe rotatable mirror produce a real image of a scale in approximatelynatural size, and another convergent system magnifies this image andprojects it on a ground plate research work is that or theGauss-Poggendorii having a reading mark. In contradistinction to type.This instrument has a mirror and a comthe instruments referred to above,in which use paratively long scale, which is viewed by means is made ofa scale approximately one metre in of a telescope beneath it andilluminated .over its length and comprising 1000 division lines, theinentire length, the field of view of the telescope strument accordingto the invention permits the containing a line mark and receiving animage use of a scale which is reduced in size to one of that part or thescale which corresponds to tenth, namely a scale thatis 100 millimetreslong the position of the mirror. It the Gauss-Poggenand whose divisionlines are 0.1 millimetre apart. dorfl instrument is not howeverpractical for If, according to the invention, also the distancetechnical apparatus, this is due to the great dis- 1 between thegalvanometer and the scale is retance between the galvanometer and thereadingduced to one tenth, so as to be in keeping with of! device and tothe additional disadvantage of the reduction in size of the scale, thescale ends the observer being compelled to read'on the scale againcorrespond to the extreme positions of the through an eye-piece. Anotherknown construcrotatable mirror. As the scale is no longer than tion, inwhich a stationary projector produces on 2 100 millimetres in this case,it is possible to prov a long scale the image of aluminous index apvideclose to the rear thereof a condensing lens' pearing in the galvanometermirror is not very which projects the incandescent body of anelecadvantageous either, especially because the obtric lamp through thescale on the rotatable server's eye must needs follow the long way ofmirror. Instead of being now made to appear this index. 25 on a groundglass plate, this scale image is used The demands to be made on agalvanometer for reading-off only subsequently to having been apparatusfor technical use, and which, so far, magnified by a third convergentsystem. This have not been iulfllled at least concurrently in thirdsystem produces the said image on a one and the same instrument, are,therefore, as ground glass plate having a reading mark. As follows: thescale to be imaged can easily be illuminated 1. Great relative accuracyor, in other words, sufliciently and in a uniform manner onacutilisation oi an image angle of approximately count of its reducedlength, the projection of the 20 which corresponds to an angle ofrotation scale image can be magnified 10 to 15 times of the mirror of10, and the reading-off on a without the results 0! the reading-offbeing imscale having as many division lines as permit a paired. completeutilisation of the relative accuracy to The convergent optical system infront of the be obtained optically by the size and the rotationgalvanometer mirror is conveniently retraversed of the mirror. by theimaging rays, subsequently to these rays 2. Instead of being compelledto view with one having been reflected by the rotatable mirror, so eyethrough an eye-piece, the observer is to be 40 that the real scale imageproduced by this conin a position to see the image with both eyes onvergent system is close to the scale. a ground glass plate, so that hishead need not The accompanying drawing shows in sectional assume anydefinite and perhaps uncomfortable elevation a constructional example ofan instruposition. ment embodying the invention. v

3. The eye of the observer is not to be required n h drawing, l 18 anincandescent p which is imaged on the revolving mirror 5 of a mirrorgalvanometer 6 by means of a condensing system having a great apertureand consisting of three lenses 2, 3 and 4. In close proximity to thiscondensing system is disposed a scale I, which is uniformly illuminatedthroughout. By another lens system 8, the scale 1 is imaged in the plane-E-'E with approximating unit magnification.

mentioned demands are fulfilled concurrently by When the scale is beingimaged, the lens system is retraversed by the imaging rays, subsequentlyto these rays having been reflected by the rotatable mirror 5. Theimaging of the scale in the plane E- E is'due to the imaging rays beingtotally reflected by a. prism 9; ;By means of an objective I I having asmall focal length and a great ratio of aperture, the scale image in theplane E-E is imaged fifteen times as great for the reading-off on aground glass plate ii, the ray path being deflected at right angles by amirror I2.

I claim:

1. In an optical system for indicating the angular deflection or themirror of a mirror galvanometer, a light source, acondenser lens system,a screen,- a reading mark on said screen, a scale on the side of thesaid condenser lens system toward said mirror, a convergent lens systemarranged in axial alignment with the light beam from the said lightsource to focus an image of the said scale in an intercepting plane withabout unity ratio, and a second convergent lens system arranged in axialalignment with the light beam between said plane and said screen tofocus upon said screen an enlarged image of the central part of saidscale image.

subsequently to reflection from system and said screen and in 2. Inanoptical system for indicating the angular deflection of the mirror 01' amirror galvanometer, a light source, a condenserlens system, a screen, areading marl: on said screen, a conver-v Bent lens system between saidcondenser lens system and said mirror rotatable about an axis parallelto its surface, a scale arranged in the focus of said convergent lenssystem on the side of said condenser lens system toward said mirror.said condenser lens system and said convergent lens system arranged tofocus an image of said light source upon said mirror, said convergentlens system arranged to be transversed by the imaging rays from saidscale and retraversed said mirror to focus an image of said scale in anintercepting plane with about unity ratio, a second convergent lenssystem between said first convergent lens axial alignment with the lightbeam from said light source to focus upon said screen an enlarged imageof the centrap part of the image of said scale formed by the said twicetransversed first convergent lens system.

GERHARD mean.

